Diarylsulfonylureas (DSU's) represent a new class of antitumor agent with a novel mechanism of action. Several analogues demonstrate high therapeutic efficacy in both rodent and human solid tumor systems. One compound, N-(5- indanylsulfonyl)-N'-(4-chlorophenyl)-urea (ISCU), currently in Phase I evaluation, is the most active agent that we have evaluated against advanced stage xenografts of human colon adenocarcinoma. Using human colon tumor models in vitro and in vivo it is proposed to elucidate the mechanism of cytotoxicity and examine the biochemical basis for therapeutic selectively for this class of agent. Preliminary data implicate mitochondria as a probable site of action. Our hypothesis is that energy dependent concentrative accumulation of DSU's in these organelles is a consequence of the pH differential across the matrix membrane, and that high concentrations of drug in mitochondria disrupt some function which leads to cell death. Using analogues with different potencies, mutant clones resistant to ISCU, ionophores and uncoupling agents, the relationship between mitochondrial accumulation of DSU's, pH dependence and cytotoxicity will be examined and the basis for sequestration established. Specific binding in mitochondria will be determined using a photoaffinity analogue. Subsequent studies will define functional changes in mitochondria both in intact cell and after isolation, that lead to cell death. The influence of proliferative status and hypoxia on cytotoxicity, and the potential to repair damage will be examined. The basis for therapeutic selectivity will be approached initially by study of the cellular pharmacology of DSU's in isolated cells from normal tissues of the mouse. Subsequently, distribution, accumulation and metabolism of analogues in xenografts of human colon adenocarcinomas sensitive or resistant to DSU's and in normal tissues of mice will be examined. These studies will facilitate defining mechanisms of action of DSU's and may identify new therapeutic targets which can be further exploited in treatment of human colon adenocarcinomas.
